Acute porphyrias are inherited metabolic disorders that cause life- threatening neurological symptoms, and are treated with intravenous heme. The objectives are to study heme arginate (the preferred preparation of heme) for treatment and prevention of acute attacks of these disorders and to determine the lowest dose that is effective biochemically. The specific aims are to determine 1) safety and efficacy of heme arginate in acute attacks of porphyria; 2) value of heme arginate infusions for preventing frequent attacks of prophyria; and 3) the lowest effective dose of heme arginate in reducing prophyrin precursor and hemopexin levels in stable patients with acute intermittent prophyria. These studies with heme arginate, an orphan product, will support an application by the manufacturer for approval by the FDA. The studies will significantly improve management of acute porphyrias in the U.S.